Home A Level Inorganic Chemistry - Core Periodicity Atomic radius down group 2

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Atomic radius down group 2

Learning outcomes

After studying this page, you should be able to:

  • describe and explain the trend in atomic radius down group 2

Atomic radius

The table shows atomic radius values for the common elements in group 2 (the alkaline earth metals).

Element Symbol Atomic number Atomic radius /nm
beryllium Be 4 0.125
magnesium Mg 12 0.160
calcium Ca 20 0.174
strontium Sr 38 0.191
barium Ba 56 0.198

Atomic radius is the distance from the centre of the nucleus to the edge of the surrounding electron cloud. It is measured or calculated in different ways, so values vary from source to source.

Description of trend

The graph shows how atomic radius varies down group 2:

  • as the atomic number increases, the atomic radius increases.
When you click on the download symbol, you will be able to download the graph as an image file or pdf file, save its data, annotate it, and print it. Note that graphs will be watermarked.

Explanation of this trend

Going down group 2:

  • there are more filled shells between the nucleus and the outer electrons …
  • the outer electrons are more shielded from the attraction of the nucleus …
  • so the electrons in the higher energy levels are further from the nucleus …
  • the atomic radius increases.

You might expect the atomic radius to decrease because the nuclear charge increases going down the group. However, this does not happen: although the electrons in the inner shells become closer to the nucleus, the factors described in the Explanation have a greater influence overall.